The invention is especially suitable in the wire reinforcement of the carcass plies and annular belt reinforcement of tires used on large trucks and earthmover-type vehicles. Such wire reinforcements or cords are normally composed of a number of steel strands which are cabled together to form the desired cord construction, each of the steel strands, in turn, being composed of a plurality of individual steel filaments or wires which are twisted together. The steel strands are designed to carry an equal share of a load imparted to the cord during the operation of the tire. Voids are inescapably formed within the cabled cord. It has been found that moisture, trapped within the tire during the building and operation of the tire, finds its way into these voids and eventually causes the corrosion of the individual steel wires. Corrosion can be prevented or greatly reduced by filling the voids or interstices of a metal cord with corrosion resistant material, such as any suitable rubber cement or adhesive, or an appropriate hydrophobic material, e.g. polyolefins, such as polyethylene, polypropylene, polybutene and copolymers of such olefins. A centrally disposed core of synthetic polyester fibers around which the steel strands are wrapped, was found highly effective in decreasing the corrosion of the steel wires. Unfortunately, such cores reduce the strength of the cord reinforcement, since the cores are simply not capable of carrying the loads that the steel strands are able to carry. A typical example of such a cord is found in U.S. Pat. No. 3,756,883 which describes a core which is purposely designed to break to allow the uncoiling of the strands that are cabled around the core. The invention is designed to provide a steel cord reinforcement with a load carrying core which does not detract appreciably from the overall strength of the reinforcement.
Briefly stated, the invention is in a steel cord reinforcement for a tire and comprises a plurality of steel strands which are cabled or spirally wrapped around a centrally disposed non-metallic core having a tensile strength which closely approximates that of the steel strands.